Welding techniques such as laser welding are being used more frequently as a means to repair and restore various types of worn components. Laser welding operations include procedures such as the welding or joining or parts and material deposition or cladding. Laser welding has found particular application in the repair of gas turbine engine components. These components are frequently expensive such that their repair, rather than replacement, is economically justified. Further the components are often made of high strength, high performance alloys such that other welding repair techniques will not service these materials, unless they are combined with other methods such as a pre-weld heat treatment. The trend is to push turbine engine components to still higher levels of performance, and thus engines will continue to see components with high strength and high performance materials. Consequently there is an ongoing need to improve the laser welding methods that will be used with these types of components.
Recently it has been found that conventional laser welding equipment will not adequately repair certain kinds of gas turbine engine components. The blisk, for example, is a development in the design of gas turbine engine components that calls for repair methods that differ from those used with previous components. Similar to the blisk are other gas turbine engine components such as the impeller and other rotor/airfoil devices.
A blisk is an integrally structured airfoil and rotor device in which airfoils are integrally formed with the perimeter of a rotor disk by, for example, integral casting. This design provides the advantage of eliminating the connection between individual airfoils and the rotor at a dovetail. The blisk, by having a unitary construction, also provides a strong mechanical connection between the airfoil region and the rotor disk region thereby allowing for a more efficient positioning of the airfoils. This results in an improved performance of the blisk in terms of weight and component size.
The development of the blisk as a gas turbine engine component has presented challenges with respect to repair strategies. Individual airfoils are now permanently attached to the rotor disk, which means that damaged airfoils cannot easily be removed for repair, as has been done with individual turbine blades. Nonetheless, blisks do have a normal life cycle and must be repaired or replaced at the end: Blisks are impacted by foreign objects such as sand, dirt, and other such debris. Blade leading edge damage, for example, is a common failure experienced in blisks. The leading edge is subject to foreign object damage or erosion after a period of service time.
The option of throwing out worn engine components such as blisks and replacing them with new ones is not an attractive alternative. Blisks are very expensive due to costly material and manufacturing processes. Consequently there is a strong financial need to find an acceptable and efficient repair method for turbine blisks.
Blisks, and other rotor devices, used in modern gas turbine engines are frequently castings from a class of materials known as superalloys. Disadvantageously, the superalloys generally are very difficult to weld successfully. Traditional repair methods have proven less than satisfactory for superalloy materials. Known welding techniques often include heating an airfoil to high temperatures, ranging from 1800° F. to 2000° F. before the welding process. However, at such an elevated temperature the airfoil may experience heat cracking and fracturing, rendering the blade unusable for further engine service. Other welding techniques similarly suffer from a lack of thermal control and provide too much localized heat during welding to render an effective repair. Superalloys are susceptible to microcracking during localized heating.
In addition to the welding challenges presented by the component material, the geometrical configuration of blisks, impellers, and similar devices also makes conventional welding very difficult. The complex geometry of the airfoil, and particularly, the shape of the leading edge, makes it difficult to deposit filler or cladding material thereon. It is often necessary to change the orientation of a welding nozzle with respect to the airfoil leading edge. However, in doing so, the nozzle or other welding apparatus may impact neighboring airfoils. The confined geometry of the airfoil thus makes it difficult to apply a laser beam to points other than the extreme outer surfaces of a blisk using conventional equipment.
Thus, laser welding performed with known designs of laser nozzles has shown the drawbacks of the prior art. In one aspect laser nozzles are bulky. They frequently include a shielding plate and a shielding gas housing. The shielding plate has been used to protect the nozzle from heat and debris generated during the laser welding operation. A shielding gas housing is the structure that collects shielding gas and allows it to be dispensed toward the weldpiece. However, these pieces of the prior art nozzles often interfere with positioning and movement of the nozzle. It would be desired to redesign a laser welding nozzle so as to eliminate these bulky and cumbersome structures.
Another shortcoming that has become apparent with known laser welding nozzles relates to the transmission of shielding gas through the shielding plate itself. The shielding plate often has small holes which allow shielding gas to pass through. However, the position of these holes can cause turbulence in the flow patterns of the shielding gas. Turbulence can degrade the quality of the inert gas shielding. It would thus also be desired to develop a laser welding nozzle that minimizes turbulence in the gas flow and improves the coverage provided by the inert gas shield.
Hence, there is a need for an improved coaxial nozzle that addresses one or more of the above-noted drawbacks and needs. Namely, a coaxial nozzle for use with laser welding is needed that is compact in size so that it may be used with parts having confined spaces and/or a nozzle that eliminates bulky structures and/or a nozzle that better directs shielding gas around the laser. Finally, it would be desired to provide an improved compact coaxial laser welding nozzle that allows laser welding repair on items for which it has previously been unable to perform laser welding repair. Finally it is desired that a nozzle be provided that, by virtue of the foregoing, therefore realizes a cost savings with respect to alternative repair methods. The present invention addresses one or more of these needs.